Conventional drywall tape typically fabricated of non-adhesive backed paper is secured over joints between sheets of drywall with a drywall compound sometimes referred to as “mud”. Prior art devices known as drywall tapers such as described in U.S. Pat. Nos. 3,960,643; 4,086,121; 4,652,331 and 5,013,380 have been developed to contemporaneously apply conventional drywall tape and mud to seal drywall joints. In these devices, tape is coated with mud as the tape is drawn through rollers or a drive wheel from a continuous roll of tape. The mud-coated tape is then applied over drywall joints and pressed into place with the drive wheel or rollers.
These prior art devices also includes a hollow storage body for receiving and storing a supply of drywall compound, an applicator head mounted to the top end of the storage body and a plunger which is moveably positioned in the storage body. Drywall compound or mud filling the storage body can be pushed by the plunger through a passageway in the applicator head to apply mud to the tape before the tape is applied over the drywall joints.
U.S. Pat. No. 4,086,121 to Ames discloses a well known prior art self-contained drywall taper. In this design, a piston slidably mounted in a hollow drywall compound-receiving body is automatically moved by means of a cable arrangement connected to and actuated by tape-engaging drive wheels on a compound dispensing front nozzle. The drive wheels must be rotated over a wallboard surface in order to force a layer of drywall compound onto a drywall tape just before it is applied to the surface. A sleeve slidably mounted on the body is moved in one direction to initially feed the tape into engagement with the drive wheels, and is moved in an opposite direction to actuate a tape cutting mechanism. A separate and additional cable and pulley arrangement is employed to selectively swing a tape creasing disk into position when applying the tape in a corner joint.
In using devices of the type described above, however, it has been found that several problems arise during use which negatively affect the maintenance costs, ease of operation, work effectiveness and taping quality. One of the chief drawbacks resides in the cable arrangement between the piston and the drive wheels which results in creating a drag force that requires substantially more operator effort in a taping operation. Any slippage of the drive wheels on the wallboard will leave a dry spot on the tape which is unacceptable. In addition, prior arrangements do not permit an operator to increase or decrease the amount of drywall compound being delivered during a taping procedure. In fact, stoppage of the prior art tool will not allow any drywall compound to be delivered. From a maintenance standpoint, the cable is liable to irregularly wind up over itself altering the rate of delivery and is prone to break so that taping operations are compromised by having to repair or replace the cable. In the same vein, this design has a complexity of parts which may require further increase in upkeep. Further, the Ames device is not readily detachable into simple assemblies so that the body is not intended to be interchangeable nor is the device easily cleaned so that working effectiveness is impaired. Moreover, the severing device is generally inaccessible and is susceptible to jamming. The creaser disc requires actuation from a lever control located remote from the actuating sleeve.
It is therefore desirable that the apparatus for applying drywall compound and tape to wallboard joints be provided with an enhanced design and a more unified control arrangement that will improve the versatility, operability, speed and efficiency of a drywall taper in all aspects of a drywall taping operation.